The invention relates to a hydraulic circuit for controlling and cooling a clutch transmission, in particular a dual clutch transmission, in particular of a motor vehicle, with two clutch cylinders and a plurality of preferably double-sided actuatable switching cylinders.
Dual clutch transmissions are preferably used in passenger cars. A dual clutch transmission generally includes two coaxially disposed transmission input shafts, which are each associated with a sub-transmission. A clutch is associated with each of the transmission input shafts, via which the transmission input shaft of the respective sub-transmission can be frictionally coupled to the output of an engine, preferably an internal combustion engine of a motor vehicle. A first of the two sub-transmissions typically includes the odd gears, whereas a second of the two sub-transmissions includes the even gears and the reverse gear.
Typically, one of the sub-transmissions is active while driving, which means that the transmission input shaft associated with this sub-transmission is coupled to the engine via its associated clutch. A gear providing a current gear ratio is engaged in the active sub-transmission. A controller determines whether the next higher or next lower gear is to be engaged depending on the driving situation. This gear which will probably be used next is selected in the second, inactive sub-transmission. When changing gears, the clutch of the inactive sub-transmission is engaged, while the clutch of the active portion is disengaged. Preferably, opening of the clutch of the active sub-transmission and closing of the clutch of the inactive sub-transmission overlap so that the flow of force from the engine to the drive shaft of the motor vehicle is not at all or only briefly interrupted. As a result of the gear change, the previously active sub-transmission becomes inactive, while the previously inactive sub-transmission becomes the active sub-transmission. Thereafter, the gear expected to be used next can be engaged in the now inactive sub-transmission.
The gears are engaged and disengaged via elements, preferably via the shift rails that are actuated by hydraulic cylinders, also known as switching cylinders, which have already been mentioned above. The hydraulic cylinders are preferably formed as double-acting hydraulic cylinders, in particular synchronous cylinders or differential cylinders, so that preferably two gears may be associated with each switching cylinder. Alternatively, single-acting hydraulic cylinders may also be provided. The hydraulic cylinders operating the elements, in particular the shift rails are also referred to as gear selector cylinders. A gear selector cylinder designed as a synchronous cylinder to which in particular two gears are assigned, has preferably three switching positions, wherein in a first switching position a first defined gear is engaged, in a second switching position another defined gear is engaged, and in a third switching position none of the two above-mentioned gears is engaged.
The clutches associated with the two sub-transmissions are also hydraulically actuated, i.e. closed or opened. Preferably, the clutches each close when hydraulic pressure is applied, whereas they open when no hydraulic pressure is applied, i.e. when pressure is relieved in a hydraulic cylinder associated with the respective clutch which is also referred to as clutch cylinder, as mentioned above.
In addition, the operation of a dual clutch transmission is known per se and will thus not be discussed here in detail.
The structure and the operation described in the preceding paragraphs preferably also apply to or are related to the subject matter of the invention.
As already indicated, dual clutch transmissions are controlled or regulated as well as cooled by a hydraulic circuit. This hydraulic circuit, or subassemblies thereof, and methods associated therewith are the object of the invention.
Conventional clutch transmissions include at least one pump for conveying a hydraulic medium and at least one pressure accumulator for receiving and providing a pressurized hydraulic medium. The hydraulic medium conveyed by the pump is supplied to the pressure store to make pressurized hydraulic medium available as needed, even when the pump is not operated, or to maintain the pressure in the hydraulic circuit. An electric motor which is operated depending on the charge requirements of the pressure accumulator is associated with the pump to drive the pump.
A clutch transmission is known in the art, for example from the German published patent application 102 43 282 A1, wherein the pressure in the hydraulic circuit is measured with a pressure sensor. When the pressure in the hydraulic circuit decreases, for example because an adequate supply of pressurized hydraulic medium is no longer provided by the accumulator, the electric motor is switched on to convey new hydraulic medium into the hydraulic circuit in order to increase the prevailing pressure therein. However, a pressure sensor in the hydraulic circuit requires a certain installation space and corresponding manufacturing costs.